1. Technical Field of the Invention
The present invention relates generally to a core pin to be placed in the mold cavity of a casting mold, such as a die-casting mold, to form a prepared hole for tapping or the like in a casting and, more specifically, to a stepped core pin having a shank to be inserted in a pin holding bore formed in a casting mold and a forming portion having a diameter smaller than that of the shank which projects into the mold cavity of the casting mold from the inner surface of the casting mold defining the mold cavity.
2. Discussion of the Related Art
The forming portion of the stepped core pin projecting from the inner surface of the casting mold defining the mold cavity of a casting mold is exposed repeatedly to the shrinking action (bending stress) of molten metal poured into the mold cavity of the casting mold during the solidification of the molten metal.
The stepped core pin is provided within the casting mold with its shank fitted in a pin holding bore formed in the casting mold and with the forming portion having a diameter smaller than that of the shank and extending from the shank into the mold cavity of the casting mold. Since the bending stress induced by the shrinking force of the molten metal developed during the solidification of the molten metal is concentrated on the base of the forming portion, the stepped core pin is liable to be broken at the base of the forming portion.
To improve the stepped core pin having such a disadvantage, Japanese Utility Model Laid-open (Kokai) No. 63-189462 proposed a stepped core pin for a casting mold having a stress relieving groove in a portion between its shank to be fitted in a pin holding bore formed in a casting mold and its forming portion extending from the shank in order to distribute the stress induced in the forming portion by the shrinking force during solidification. This previously proposed stepped core pin, however, has not been particularly effective in obviating stress concentration because a portion of the shank contiguous with the base of the forming portion is fitted closely in the pin holding hole of the casting mold.
Accordingly, it is an object of the present invention to provide a stepped core pin having a forming portion to be projected from the inner surface of the casting mold defining a mold cavity into the mold cavity, designed so that no bending stress resulting from the shrinkage of molten metal poured into the mold cavity during solidification will be induced in the base of the forming portion, which is capable of enduring repetitive stress (bending stress) induced by the shrinking action of the molten metal poured into the mold cavity during solidification, and which is capable of being serviceable for a long period of use without breaking.
Other objects and advantages of the present invention will become apparent from the drawing and specification which follow.